Unitary range, azimuth, and elevation alignment indicator for radar systems



April l2, 1949. K. KING ET AL 2,467,319

UNITARY RANGE, l-xZUiUJ'T'L- AND ELEVATION ALIGNMENT INDICATOR FOR RADARSYSTEMS Filed May 2, 1945 2 Sheets-Sheet l H Mm KW LN /NVEA/Toes w. m mT A April 12, 1949. K L. KING ET AL 2,467,319

UNITARY RANGE, .AZIMUTH, AND ELEJATION ALIGNMENT INDICATOR FOR RADARSYSTEMS Filed May 2, 1945 E 2 sheets-sheet 2 F/ G. 2 /oo /oo L L v 20a 7,08 v 2/0 205 .foe

F'G. ,00 4 v [00 F/G 5 NAA/6E r600,95 C TE D RANGE E L E V4 TON ELEVAT/ON CORRECTED AND AZ/NUTH 'CONECTE A T TOR/VE lf.

/N VEN TORS Patented Apr.' 12, 1949 TION ALIGNMENT INDICATOR FOR RADARSYSTEMS Kenneth L. King, Mountain Lakes, and William T. Wintringham,Chatham, N. J., asslgnors to Bell Telephone Laboratories, Incorporated,New York, N. Y., a corporation of New York application May 2, 1945,seria1No.591,5o4

. 1 This invention relates to object detecting systems employing energyreflection and adapted for 2 claims. (ci. 343-11) radar lbombsight, orgun and searchlight directlng services and the like. More particularly,it

relates to the improvement of such systems to the end that thesimultaneous precise alignment of the system in range, elevation andazimuth with respect to a selected target will 4be facilitated. Insystems of ythis general class in the prior art it has been customary todisplay the range indi- .cations upon one indicating device (usually acathode ray oscilloscope) and to display elevation and azimuth(directional) indications upon at least one and in some cases twoadditional indicating devices. This necessitates continuously checkingthe indications on at least two, and frequently on three, indicatingdevices, in order to be certain that the'object detecting system ismaintained so as to provide accurately the range, elevationv and azimuthof a selected target.

Since these systems are commonly employed to facilitate precisionbombing from a rapidly-moving aircraft or to follow such rapidly movingand' elusive targets as modern military aircraft the provision of asystem which will present on a single indicator, a simple readilyinterpretable unitary indication showing at a glance whether the systemis accurately adjusted in range, elevation and azimuth with respect to aspecific selected target represents an importantadvance in the art.`vThe arrangements of the invention are also highly desirable for use incivilian aircraft radar `navigational systems, since, for such sys'-tems it is not usually practicable to provide ad-v ditional crew membersto operate the radar equipment and the normal crew members have manyother indicating devices to which they must also devote attention.

It is therefore the primary object of this invention to provide anobject detecting system which will provide a simple, readilyinterpretable, unitary indication of whether or not the system isaccurately adjusted to the range, elevation and azimuth of a specicselected target.

In an illustrative system of the invention to be described hereinafter,the desired objective is obtained by superimposing a range trace of thetype having a range-step, upon a spot indication of the type normallyshown on a combined train (azimuth) and elevation (directional)indicatorcommonly employed in modern gun pointing object detectingsystems, such for example,

as that disclosed in copending application of O. E.

plication has matured into United States Patent 2,426,182, grantedAugust 26, 1947, The position of the range step with respect to thesignal indication will then show whether the range setting,

is correct and at the same time the position of the signal indicationwith respect to the-screen cenyter will indicate whether the adjustmentsof train (azimuth) and elevation angles are correct with respect to theselected target. known 'in the art, and as is illustratedv and explainedin the above-mentioned application of O. E. De Lange, a .range trace isa line traced by the ray of the oscilloscope indicator of afpulsereflection type range determining system, the ray beingsynchronized to start the traceat a predetermined instant with respectto the instant of emission of an exploratory energy pulse and totraverse the path of the trace in accordance with a predetermined timeschedule, such, for example, as a linear law of variation with time,whereby the position of the ray at any instant along the tracecorresponds to a definite predetermined range.' To facilitate rangemeasurements, it is common practice in the art to provide apparatuswhich produces a range index or range step, which is simply a definite,readily identifiable, discontinuity in the range trace, such as a smallVertical step, the position of which along the trace is controlled bythe adjustment of the range unit. As is well known in the art, a rangeunit is a continuously adjustable delay device having a calibrated dialvor counting mechanism associated therewith, arranged to provide therange directly in convenient units, such as yards, The range unitfunctions to-delay a pulse obtained from the circuit which pulses oractivates the transmitter. rectly as a range index or, alternatively,can control the formation of a range step of any desired character.Whatever form of range index is employed, it can be brought, Ibyyadjustment of the delay of the range unit, into a denite predeterminedtime relation (usually into substantial coincidence) with respect to theindication resulting from receipt of reflected exploratory pulses fromany selected reflecting object. The range 'of De Lange, Serial No.504,577, led October 1,

the selected object can then be read directly -from the above-mentionedcalibrated dial or counting mechanism of the range unit, and the rangingsystem is then said to be in alignment withthe selected object. y

Other objects and advantages of the invention will become apparentduring the course of the following description of an .illustrativesystem ofv the invention and from the appended claims.

As is wellv The delay pulse may `be used di- The principles of theinvention will be more readily under: '.ood in connection with thefollowlng detailed descriptionbf a preferred illustrative embodimentthereof, shown on the accompanying drawings in which:

Fig. 1 shows in block diagram form a system illustrative of theinvention; and

Figs. 2 to 5 inclusive show typical range and directional indications onthe indicator of the system of Fig. 1 and illustrate one sequence ofsteps which may be taken to effect the proper final alignment of thesystem.

In more detail in Fig. 1, modulator 30 provides sl ort, squared-top,high voltage pulses to radio transmitter 28, causing it to generatesimilar short pulses of radio frequency energy. These latter pulsespass, through TR (transmit-receive) box 24 and transmission line 20, toantenna feed and pick-up 4device I 0, which projects them againstparaboloid reflector I2 from which they are reflected in a highlydirective beam to strike remote objects Within the path of the beam inaccordance with standard radar technique now well known to those skilledin the art.

TR box 24 is preferably of the well known resonant cavity type having agas tube connected across points of substantially different potential,the cavity being effectively in shunt across the input to converter 26.The high-power pulses from the transmitter then serve to break down thegas tube thus effectively shorting the input circuit to converter 26 andprotecting it from the transmitter energy. Upon the cessation of eachtransmitted pulse the gas tube recovers substantially instantaneouslyleaving the converter 26 fully sensitive to the relatively feeblereceived reflections of the transmitted pulse.

Antenna feed and pick-up device IIJ is preferably of the horn type ofradio wave projector. Alternatively it can be a small dipole antennaequipped with a small reflector to direct the radiated energy toward thereflector I2. It should be located at the focal point of reflector I2,on the normal axis of the reflector.

Reflector I2 is tilted slightly from its normal axis and is nutatedabout its normal axis -by rotation substantially as shown in UnitedStates Patent 2,083,242, issued June 8, 1937, to W. Runge, Fig. 2. MotorI6 provides the power for effecting rotation of antenna reflector 4I2 ataconvenient speed, for example, at 30 cycles per second.

Motor I6 also drives a two-phase sine Wave generator I8, known in theart as a lobing generator when used as shown in Fig. 1, since the phasesof the sine waves generated are employed, as will presently appear, toindicate at any instant the position of the antenna lobe.

The antenna system II, including the motor I6 and lobing generator I8,is preferably mounted so that it can be turned in azimuth and tilted inelevation to detect and follow targets such as aircraft. It can, forexample, be mounted as for antenna systems shown in Patent 2,231,929 toJ. Lyman, issued February 18, 1941.

Y Received reflected pulses, l. e., echoes of the 4transmitted pulsesresulting from reflection by the object or objects to be detected andlocated, are directed to device I0 by reector I2 and follow transmissionline 20 to TR box 24. Those returning during the intervals that thetransmitter 28 is passive, Will freely pass through TR box 24 toconverter 26.

Converter 26 can be of the vacuum tube type or of the crystal type,Iboth of which are well known 1n the art. It includes a beatingloscillator and converts the radio frequency pulses into a Corlvenientintermediate frequency which is usually less than 100 megacycles. Anautomatic frequency control 32 is preferably included to slightly varythe beating oscillator frequency so that the resulting intermediatefrequency does not sensibly change even though the frequency of thetransmitter 28 should drift slightly from its normal frequency. Sucharrangements are of course well known in the art. It is, of course, notessential.

The intermediate frequency is then amplifled in amplifier 36 anddetected to obtain the video frequency. The latter frequency is furtheramplied in video amplifier 46, the output of which is applied to thecontrol electrode 58 of cathode ray oscilloscope 56. This arrangement,of course, results in the intensity modulation of the ray. i. e., theproduction of a momentary increase in the brillance of the ray, at themoment a video signal is impressed upon electrode 58.

A portion of the output energy of amplifier 46 is fed back through aconventional automatic gain control circuit 38 to control the gain ofthe I. F. amplifier 36 and a second portion of the output of amplifier46 is furnished to amplitude modulation detector 48 for purposes to bedescribed presently.

Amplier 46 is also preferably gated, i. e., permitted to transmit onlythe reflected signal or signals which arrive back at the antenna withina predetermined time interval which is predetermined adjustably by thefollowing circuit.

A portion of the energy pulses from modulator 30, which serve toenergize transmitter 28 as described above, is also provided to rangeunit 44. The range unit is adjustable to delay the pulses from modulator30, by a time interval which can |be varied between that correspondingto the receipt of energy reflections from an object at the shortestrange to be measured to that corresponding to the receipt of energyreflections from an Iobject at the longest range to be measured by thesystem and in conjunction with range gate circuit 42, provides at theoutput of circuit 42, a squared-top pulse the center point of whichcorresponds tothe reading of the range as shown on calibrated counterdials which turn as the range unit is adjusted.

The width of the squared-top pulse is such that it corresponds to asmall portion only, of the total range to be measured by the system. Forexample, many systems of the general type illustrated in Fig. 1 aredesigned to measure ranges up to 40,000 yards maximum and for these, arange gating pulse of approximately 2,000 yards (about 10 microseconds)has been found suitable.

It is obvious that the arrangements just described permit the selectionof any portion of approximately 2,000 yards in width, for example, ofthe total range by simply adjusting the range unit to cause the rangegating pulse to occur 1at the position corresponding to the desiredporion.

The pulse from range unit 44 ls furnished to three units namely, therange gate circuit 42 which can be a conventional multivibrator circuitproviding the above-mentioned squared top pulse in response to thereceipt of each of the delayed pulses from modulator 30, via range unit44, the sweep voltage generator 50 and the fixed delay circuit 52.

AThe squared top pulse from the range gate circuit 42 furnishes a Ibiasto video-amplifier 4B Which overcomes a blocking bias in a grid-cath- 75ode circuit of the amplifier. This permits reflected signals coincidentin time with the pulse from range gate circuit 42 to pass through and beamplied by amplifier 46, other pulses being excluded because theamplifier 46 is normally blocked. Such arrangements are, of course, wellknown in the art.

The sweep voltage generator 50 responds to the pulse from range unit 44by generating a sweep voltage, preferably of the well-known linearsawtooth type, which is applied as shown in Fig. 1 to lthe horizontaldeilecting vplates 60 of oscilloscope 56 and produces a horizontalsweep, or trace, the duration ofl which corresponds to the width of thepulse provided by range gate circuit 42. (usually about 2,000 yards) thelcenter point of the sweep corresponding to the range registered on thecalibrated counter dials of the range unit as previously described.

Fixed delay circuit 52 introduces a timedelay precisely equal to halfthelength of the pulse provided byv gate circuit 42, the output of delaycircuit 52 being connected to range step generator 54.

Range step generator 5d responds to the leading edge of the pulsereceived from unit 4d -by way of delay circuit 52 and provides a, rangestep, or sharp vertical step, as an index markin the horizontal rangetrace, when its output is impressed, as shown in Fig. l across thevertical delecting plates 62 of oscilloscope 56. Any other welldeneddiscontinuity in the trace, such as a notch or pedestalsuperimposed upon the range trace could, obviously, serve as an indexmark. The simple vertical step, however, lends itself very well to thepurposes of the invention, aswill ibecome apparent hereinunder. Rangestep generator 54 can be any one ofthe numerous electronic alignmentwith the object. initially positioned so that one phase reaches itsmaximum value of one polarity when the nutation of reflector I2 hasdisplaced the antenna lobe to itsl maximum vertical angle, then themaximum value of the opposite polarity of that phase will correspond tothe minimum vertical angle of the lobe and the other phase will have amaximum value of one polarity for the maximum lobe angle to the rightand a maximum value of the other polarity for the maximum lobe angle tothe left.

voltage step-generating circuits Well known to those skilled inthe art.By way of example, it can be of the form shown and described in detailin the application Serial No. 491,791, llled June 22, 1943, by L. A.Meacham, circuit 28 of Figs. 1 and 3.

Meachans application has maturedl into United States Patent 2,422,204,granted June 17, 1947. The output of the amplitude modulation detector48 is passed through a lllter 40 the function of which is to select thelobing frequency, i. e., the frequency of the amplitude modulation ofthe received reflected pulses if the target from which reflections arebeing received is not precisely on the axis of the antenna system asdescribed above. This frequency is, of course, determined by the rate atwhich the reflector I2 is nutated andis commonly- 30 cycles per secondso that lilter iIJ should freely pass'30 cycles per second, for example,and exclude all other frequencies. The output of filter 40, togetherwith the twophase output of lobing generator I8 are furnished to lobingmodulator 34. I The two-phase output of generator I8 comprises, as'mentioned above, two-'sine waves, mutually in quadrature, i. e.,displaced 90 degrees in phase with respect to each other, and denitelyrelated at any instant to the angle of reflector I2. The frequency ofthese sine waves and the frequency of the amplitude modulation are, aspreviously mentioned, the same as thefrequency of the nutation cycle ofreflector I2. The phase or' the amplitude modulation, however, isdetermined by the direction in which a specific reflecting object isdisplaced with respect to the normal axis of the antenna system. Henceits phase can obviously be employed to indicate the direction in whichthe axis of the antenna system must be moved to bring it into Each phaseof the generator i8 is then compared with the phase of the amplitudemodulation passing through lllter d0 by lobing modulator 3 which can beofthe type described in detail land'shown in Fig. lof theabove-mentioned application of O. E. De Lange and which employs for eachof the two necessary phase comparisons a standard balanced phase'modulator. That is, lobing modulator 36 comprises two standard balancedphase modulators which provide in a manner weil known to the art andasdescribed in detail in the De Lange application mentioned above, twovoltages, one indicative of the phase relation between the amplitudemodulation and one phase 50 and step generator 5B are turned off,but theremainder of the system is operating and that deflections are beingreceived from an object Iwhich is slightly displaced from the normalaxis of the antenna system a so-called spot indication will result, thespot' being displaced from the center point of the oscilloscope atanangle corresponding to the direction in which'the object is displacedfrom the normal antenna axis and at a distance which is substantiallyproportional to the amount the object is displaced. I

if thesweep and step generators 50 and 54 are then turned on, a rangetrace with a range step in the center thereof will be added on theoscilloscope screen and the spot will be elongated horizontally becauseof the lateral sweep of the range trace. The position of the elongatedspot on the range trace with respect to the range step will indicatewhether the range unit has been adjusted properly to provide an accuratereading of the range of Athe object from which the reilections are beingreceived. The entire range trace will, of course, be displaced by thevoltages provided by modulator 3A in the event that the object is not onthe normal axis of the antenn system as described above.

A num-ber of illustrative oscilloscope indications for the system ofFig. l are shown in Figs. 2 to 5 inclusive and will be discussed below.

A range unit which also includes a gating pulse circuit and a range'stepgenerating circuit, all of which are suitable for use in the abovesystem is, for example, described in detail in the afore-v mentionedcopending application, Serial No.A4

491,791, led June 22, 1943, by L. A. Meacham, n

Generator I8 lsv 1indetai'l. a suitable loting.Y modulator and illus-:1`

tober 1;, 1943, by OLE. DefLange;assignortoape 1 plicants assignee..[The De Lange rapplication .also f ..disclosesa simple class A.indicationl andap- :1 1 1 paratus 1for1 obtaining rit, whichis.ofinterest in. .thatit illustrates the use'of a :range trace :hav-

. ing a range step. The so-called class A'indica l 1."noved, byadjustment ofl the range unit, until therange. step aiigned with, :theleading edge. f of. a targetindicationi-interest.. Thetarget injdications inthe system :disclosed lby De ALange comprise, for :thefclass .AF presentation, vertical 1 .plps1 .or 1 deflections caused byimpressing :the

. received lreiiectedl pulses upontbevertical de1-1 .ectingplatesof.tlieoscilloscope.1.1.1 L i i 1 An objection tonie system disclosed: in'the De Lange application is that two Aoscilloscopes.must

' f 3 be watchedv inorder to .determine whetherithelob-A f l 1 1Applicants system,A as will appear from the :fol-1 1 1 lowingdescription yof Figs. 21 to '5 inclusive lpro-1 .yides,. upon `ra.single: osciliosciope, a unitary; indi- I cation from whichalignment-@,orlack-of it, 1in :both

. 1ject detecting'systemis precisely aligned in range' i 1 and directionwith respect to a particular selecti-k 1.

. y:50i 1' range'anddirection are immediately/'apparenti i Fig. 2,1.elongated :bright spot l203. appears i 1 .position yof the' :normaliantenna; laxis in? azimuth lower: portions: of the range trace,lrespectively,

To correct the range setting the` range unit is adjusted until theelongated indication coincides with the range step as shown in Fig. 3where 308 and 3 I 0 represent the desired coincidence, 306 being therange trace.

To correct the elevation the normal antenna axis is depressed until theupper and lower portions of the range trace 406 are coincident withlines |02 and |04 respectively as illustrated in Fig. 4. 1

Finally to correct the azimuth alignment the normal antenna axis isturned to the left until the vertical center line bisects the elongatedindication 508 and the range step 5I0 which were previously brought intocoincidence as described above.

Obviously, the` corrections described above can be performed in` anyorder desired, the above sequence being entirely fortuitous andillustrative only. Also, where as is sometimes the case, threeandlhorizontal lines l'02, 104 represent tlielposi-r j'1 tions: whichshould be assumed by the upper and 1 operators are assigned, one each,to maintain This is satisfactory for distant and slowly moving targetsbut the delay entailed, though only momentary, may prove disastrous inanti-aircraft defense.

.-shifthis attention other. 1 y 1 V Numerousother arrangements withinthe spirit skilled in the art.l

; Whatisclaimedisa' 1 said: beam from'remote objects, means for del twosine` wave :voltages :and yobtaining two voltf Q ages indicativel jof:the 1 phase relations :betweeny 1 said combinedvoltages and theamplitude of said- `ja'moli-'tuile modulation voltage., al .cathode rayin f j.A

1 dicator. lhavingA ray intensity controlling. 'means connecting to theoutput of said receiving means, and horizontal and vertical deflectingmeans, said two voltages, indicative of the phase relations, beingimpressed upon said horizontal and said vertical deflecting means,respectively, means for generating a linear range sweep voltagesynchronized with the emission of pulses by said system, said ran"gesweep voltage being impressed upon said horizontal deflecting means toestablish a range trace on the screen of said oscilloscope, means forgenerating a range step Voltage synchronized to coincide with the centerpoint of said range trace, said range step voltage being impressed uponsaid vertical deecting means, and means for adjusting the phase relationof lsaid linear range sweep and said range step voltage to bring saidrange step into time coincidence with an indication on said oscilloscopescreen resulting from the reception of refiected pulses from a reectingobject whereby when said indication is centered on said range step andsaid range step is centered on the screen of said oscilloscope a unitarypositive indication that the system is aligned on said reflecting objectin range, azimuth and elevation is obtained.

2. In a pulse-reflection object-detecting and ranging system, meansadjustable in azimuth and elevation for emitting a highly directive beamof energy pulses, means for receiving reflections of said pulses from anobject within the region throughout which the beam is projected at eachinstant, means for rotating the axis of said beam regularly about areference axis, said beam axis being maintained at a constant smallVangle of less than ve degrees with respect to said reference axisduring said rotation, means for generating two sine waves having a phasedifference of degrees and frequency equal to that of the rotabandscpeofthe inventionwiltoccurftoitliosef`l f tion comprises asimplehorizontal trace onthe '1 The invention'is' denedin'thefollowingclaims..

oscilloscope .along 'Which-a lrange step :can1be1'1' 1 l .1. In aradioenergy reflection oblectdetect-z 1 ;k ing and ranging system 'of theltype employing an 1 antenna adjustable :in azimuth and elevation and fleavingl a highly .directive pulsed beam, fthe' axis 1 i 1 1 of saidbeambeingzdisplaced'by asmaliangle' 1:

:fwithrespect to thenormal'axisof saidiantenna f system,l means forrotating the axis of saidbeam i i g 1 f about the normal axis of saidlantenma.: ata sub-l 1 ;'stantiallyconstantlow frequencyrate, means forygenerating locally: ltwo i sine 1 Waves having zthe 1' E same lowAfrequency: as that loi thebeam rota'. tion, zsaidftwofsine wavesbein'gdisplaced .90de- :1 :grees in phase with respect: to'eachother and f 1 f1 denitely related: in' :phase to the .vertical .and :horizontalmotions= of: said. beam respectively, means -for kreceiving fand;ydetecting reflectionsr or 1 1 I `f tectinggandsegregating. amplitudemodulation of 1, `Said received reflections or the saidA low frequency,1 j means lfor separately combiningsaid lamplitude on renee trace 20.6,whichtrace'inciudesrange1-IImedulabcnfrequeneyroltagewith:cachotseid1step 2&0. Vertical centerline lllrepresentsthe 9 tion of said beam axis,means for detecting amplitude variations of the received reiiectedpulses, means responsive to said two sine waves and said detectedamplitude variations to provide two Voltages representing deviation ofsaid reference axis from the said reflecting object in two orthogonallyrelated directions, respectively, a cathode ray oscilloscope having aray intensity control means connecting to the output of said receivingmeans and horizontal and vertical deecting means, said two voltages,representing deviation of said reference axis, being impressed upon saidhorizontal and said vertical deilecting means, respectively, means forgenerating a linear range sweep voltage synchronized with the emissionof pulses by said system, said range sweep voltage being impressed uponsaid horizontal deecting means to establish a range trace on the screenof said oscilloscope, means for generating arange step Voltagesynchronized to coincide with the center point of said range trace, saidrange step voltagev being impressed upon said vertical deflecting means,and means for adjusting thel phase relation of said linear range sweepVoltage and said range step voltage to bring said range step intocilloscope screen resulting from the reception of reflected pulses froma reflecting object whereby when said indication is centered'on saidrange step and said range vstep is centered on the screen of saidoscilloscope a unitary positive indication that the system is aligned onsaid reflecting object, in range, azimuth and elevation is obtained.

KENNETH L. KING.

WILLIAM T..WINTRINGHAM.

REFERENCES CITED The following references are of record in the iiie ofthis patent:

UNITED STATES PATENTS Great Britain Aug. 3, 1943

